Officials say Burundi's environment minister has been shot dead, in a country where political turmoil over president Pierre Nkurunziza's extended term has led to political killings.

Police spokesman Pierre Nkurikiye said Sunday Emmanuel Niyonkuru was shot as he arrived home Saturday night. Nkurikiye says three people have been arrested including the minister's watchman and his security detail.

In a tweet, president Nkurunziza confirmed the killing and said "this crime will not go unpunished."

Burundi has faced widespread international criticism over the deadly political turmoil that followed Nkurunziza's pursuit of a third term last year, which many in the country called unconstitutional. Hundreds have been killed in streets protests, an attempted coup, rebel attacks and seemingly tit-for-tat killing between government and opposition supporters.